Such a device is already utilized in practice for fixing the lumbar and the lower thoracic vertebrae and is described, for instance, in French patent application 2,642,642. The hook of each fixation element, which is U-shaped for this application, extends between two vertebrae from a point between the spinous processes and the transverse processes of a vertebra in the direction of the spinal canal. When a fixation element is thus arranged, the substantially block-shaped body is disposed against the exterior of the vertebra located above the hook. Two fixation elements arranged above each other and thus attached to the vertebral column are connected together by means of a rod. The securing means is situated in cortical bone only at the first vertebra contact surface and for the rest the securing means extends into spongy bone, which is rather weak. The drawback of this is that the securing pin can only transmit a minor couple to the vertebra and will loosen in the course of time.
As regards the fixation of the cervical and upper thoracic vertebrae, however, the space between the spinous process and the transverse processes for accommodating the block-shaped body is lacking and further the bone mass of the vertebrae is too small for the hook to be arranged between the vertebrae in the manner described. The fact is that the diameter of the spinal canal relative to the outer diameter of the vertebrae is much greater in the cervical and upper thoracic vertebrae than in the lower thoracic and lumbar vertebrae.
For that reason, when fixing cervical and/or upper thoracic vertebrae, which is for instance necessary in the case of fracture or congenital disorders leading to deviation of the cervical and/or thoracic vertebral column, heretofore a makeshift fixation has been effected with plates, screws, wires and the like. A disadvantage of this makeshift fixation is that screws, for instance, weaken the cervical and thoracic vertebrae and that a positive result of a surgical treatment for realizing such makeshift fixation cannot be guaranteed for a prolonged time.